When the water retaining ability or barrier functions of the horny layer are weakened by some internal or external reasons, the skin suffers from various troubles accelerating skin roughness or aging. Lowering in the water retaining ability and barrier functions of the horny layer can also be recognized in the roughened skin resulting from various skin diseases such as atopic dermatitis, psoriasis or xeroderma. Therefore, the maintenance • reinforcement of the water retaining ability and barrier functions of the horny layer are highly important for our healthy daily life.
With the foregoing in view, the present applicants found, as a dermatologic preparation for external application having effects of basically improving (maintaining, reinforcing) the barrier functions of the horny layer, dermatologic preparations for external application containing amide derivatives represented by the below-described formula (2) and applied for a patent (Japanese Patent Laid-Open No. Hei 4-12825).
(wherein, Ra represents a linear or branched, saturated or unsaturated C10-40 hydrocarbon group, Rb represents a linear or branched, divalent C3-39 hydrocarbon group, and Rc represents a hydrogen atom, a linear or branched, saturated or unsaturated C10-40 hydrocarbon group or an acyl group).
Although such amide derivatives bring about excellent effects as described above, their solubility in a base ingredient or stability therewith is not always sufficient. There is therefore a room left for improvement in miscibility or mixing stability of the derivative to be incorporated in a dermatologic preparation for external application. These amide derivatives are accompanied with another problem that necessity of multi-stage reaction upon preparation inevitably leads to a rise in the production cost.
An object of the present invention is to provide a composition for external application which is capable of basically improving the water retaining ability and barrier functions of the horny layer, excellent in miscibility and mixing stability, and available efficiently at a low cost.